1. Field of the Invention
The present invention relates to a ventilator unit utilizing heat recovery, particularly of the type for installation in an outside wall of a room to be ventilated.
2. Prior Art
The most common way of ventilating rooms in a large building is through a central ventilation system installed in the house or building, wherein air ducts lead from the central installation to the various rooms in the building. The system provides air conditioning as well as heat recovery, filtering, heating, cooling and humidifying.
The incoming conditioned or fresh air is guided through the system of ducts to the various rooms and is blown into the rooms through vents. The used air is drawn out of the room through the same system via a separate system of ducts and exhausted to the outside.
Another common method is to install separate ventilator units in the rooms to be ventilated. This does not require the installation of a system of air ducts in the building, and is often preferred in existing buildings where the installation of air ducts would be difficult and costly. The best location for the ventilator unit is at an outside wall of the room so that air from the outside may be drawn into the room through an opening in the outside wall. In winter, the outside air will be cold and will have to be heated to approximately room temperature before being blown into the room. The used air is often vented to the outside at room temperature, that is, without first having been cooled.
The heating of the incoming air can be reduced significantly through heat recovery, whereby the heat from the air being exhausted is transferred to the incoming cold air. Plate heat exchangers have most commonly been used for this purpose, being both structurally and functionally simple for small room-size ventilator units of this type. The incoming air is blown into the room with great force through a grating in the top plate of the unit. The incoming air mixes with the air in the room with a stirring effect, so-called agitator ventilation. The drawback of agitator ventilation systems is that the pollutants found in the inside air are dispersed about the room and are not vented out until they happen to reach the vicinity of the unit's exhaust vent. Therefore, substantial quantities of fresh air are required for this ventilation system to function adequately, and this in turn results in drafts which may be a problem for people in the room when the air is being blown about with relatively great force. Ceiling light fixtures may also have an adverse effect on the direction of air flow in the room, increasing the drafts.
If it were possible to reduce the amount of incoming air, the size of the unit could also be reduced. Alternately, even if the unit were the same size, the air ducts could be made smaller, which would reduce noise and enable the various components in the unit to work more efficiently. For example, the plate heat exchanger would operate more efficiently, i.e., it would be able to transfer more heat from the used air to the incoming air.
A general problem with the use of plate heat exchangers is that when the outside air is cold, say, a couple of degrees below freezing, frost will form on the lamella in the exhaust air flow ducts, and these must be defrosted in order to maintain the heat recovery effect. This can only be done by stopping the unit until the ice has melted or by opening a bypass valve which causes the incoming air to bypass the plate heat exchanger. During such periods an auxiliary heating element must take care of the entire heating function, since the plate heat exchanger will no longer be operative. The heating aggregate therefore has to be larger in size and capacity than would ideally be necessary, assuming the plate heat exchanger were in constant operation. The melted ice must also be drained off, which means that ventilator units requiring defrosting must be connected to a draining outlet.
Plate heat exchangers have substantially lower efficiency than other known heat recovery systems, for example rotary heat exchangers, which represent a regenerative heat recovery system and which, unlike plate heat exchangers, also are able to transfer moisture as well as heat. Rotary heat exchangers, which are mainly used in large ventilator systems, are relatively complicated structurally and are much too expensive to be used in small room-size ventilator units.
Another type of regenerative heat recovery system is a periodic heat exchanger, in which the respective streams of air alternate between two equal regenerator masses. The prior art periodic heat recovery units, however, are not suitable for use in small ventilator units intended for ventilating a single room.